The present invention relates to pressure switches of the type having a pressure-responsive member, typically a diaphragm movable in response to changes in a fluid pressure signal to actuate and de-actuate an electrical switch. Pressure switches of this type are typically employed for sensing relatively small changes in relatively low level pressure signals. A well known application of such pressure switches is that of sensing the pressure head resulting from the water fill in a washing machine for actuating or de-actuating an electrical switch to shut off the electrically controlled fill valve in the event of overfill. Pressure switches are also employed in washing machines to control the amount of water flow in response to a user selected level.
Pressure switches for the aforesaid appliance applications typically have an externally movable member or lever pivoted for movement to adjust the preload of a spring within the pressure switch for changing the switch actuation points. Various types of adjustment mechanisms have been employed, such as rotary cams and sliding cam mechanisms. In pressure switches employing a sliding type cam mechanism, it is common to provide a metal mounting bracket on the pressure switch housing which bracket has attached thereto a plastic slider which has lugs therein received through a slot in the bracket with a cam surface provided on the edge of the slider for contacting a movable lever on the pressure switch. Referring to FIGS. 6, 7, and 8, a known pressure switch indicated generally at 10 has a housing 12 which contains the sensing diaphragm responsive to pressures through signal port tube 14 and also contains electrical switching mechanism. A plunger 16 extends externally of the housing and is movable for adjusting the preload on an internal spring for changing the setting of the pressure switch. A metal mounting bracket 18 has a right angle flange 20 which is attached to the switch housing 12 for securing the bracket thereon. Bracket 18 has an elongated slot 22 formed therein with an enlarged portion 24 at one end thereof. A plastic slider 26 has a pair of spaced lugs 28 provided thereon which are inserted through the enlarged portion 24 of the slot and guide the slider on the edges of the slot 22. Slider 26 has a knob 30 thereon for facilitating user manipulation.
Slider 26 has a cam surface 32 formed on the edge thereof which engages a lever 34 which is pivoted on the upturned portion of flange 20 of the bracket by tab 36 engaged therewith and biased thereagainst by spring 38. An adjustment screw 40 is threaded through the lever 34 to contact the end of plunger 16 for effecting movement thereof to change the preload internally on the switching mechanism.
A slipper spring 42 has the ends thereof engaged through slots 44 formed in bracket 18. The slipper spring 42 provides frictional drag between the bracket and slider 26 to prevent the forces of the lever 34 acting against cam surface 32 from moving slider 26 once it has been placed in a desired position. The length of slipper spring 42 is chosen such that when the slider 26 is positioned as shown in FIG. 8, at the end of the cam surface 32 any contact of the lever 34 by the steep ramp portion 46 on the slider 26 effects movement of the slider in a rightward direction to seat the lever 34 at the end of the cam surface 32.
The arrangement of the prior art devices has resulted in unsatisfactory sliding operation of the member 26 in view of the close spacing of the lugs 28 required to give the amount of necessary movement of the slider in the available length of the slot 22. If the lugs 28 are spaced further apart, the slot 22 is required to have additional length and the bracket becomes prohibitively large extending beyond the envelope of the switch housing by an amount which requires additional space for mounting the unit 10.
Furthermore, the close spacing of the lugs has resulted in a tendency for the slider to rotate in the slot and bind during user movement of the slider.
It has thus been desired to find a way or means of providing an adjustment mechanism for a pressure switch which provides ease of adjustment for the user and which is compact and low in manufacturing cost, yet provides stable and smooth adjustment without binding.